The present invention relates to a method and a device for estimating a transverse acceleration at an axle of a semitrailer or trailer of a vehicle combination, in particular of an articulated vehicle combination, as well as a method for implementing a braking action on a semitrailer/trailer.
In operating dynamics, handling properties may be defined as the total performance of the system xe2x80x9cdriver-vehicle-environment.xe2x80x9d Criteria for assessing the operating dynamics may include, for example, the steering-wheel angle, the transverse acceleration, the longitudinal acceleration, the yaw velocity, as well as the float angle. Additional information is used to clarify specific handling properties, e.g., the forward velocity and transverse velocity, the steering angle of the front or back wheels, the slip angle at all wheels, as well as a steering-wheel force.
In German Published Patent Application No. 41 21 954 is discussed a method for determining the yaw velocity and/or the transverse velocity of a motor vehicle, which involves determining the vehicle""s relevant quantities of motion using a minimum number of sensors.
For the electronic stability program (ESP) of articulated vehicle assemblies, braking-action strategies for preventing skidding are available, with such braking actions always being carried out at the towing vehicle. At present, it is believed that there are no satisfactory strategies for braking actions on a semitrailer or trailer of an articulated vehicle combination.
An electronic stability program for an articulated vehicle combination is used, for example, to stretch the articulated vehicle combination by braking the semitrailer or trailer when the towing vehicle is being oversteered, thereby making it possible to stabilize the towing vehicle and to prevent the articulated vehicle combination from jackknifing. However, such a braking action can reduce the lateral guiding force of the semitrailer/trailer axle so that, when cornering at a high transverse acceleration, there is the danger of the semitrailer or trailer breaking away (a so-called trailer swing). To prevent this, the braking action on the semitrailer or trailer should be carried out as a function of the transverse acceleration at the semitrailer/trailer axle. Measuring such a transverse acceleration at the semitrailer/trailer axle using suitable sensors may be relatively expensive, since, with respect to conventional articulated vehicle assemblies, additional and expensive sensor elements may be necessary. Such a procedure may be impractical, since a towing vehicle may change semitrailers or trailers, which are differently equipped.
An object of an exemplary method of the present invention is to provide a method on whose basis the transverse acceleration at the semitrailer/trailer axle is capable of being approximated in a simple and cost-effective manner.
Using the exemplary method according to the present invention, it is believed that the transverse acceleration at the semitrailer/trailer axle may be estimated in an uncomplicated manner, without additional outlay for sensors, i.e., solely on the basis of the measured quantities measured or determined at the towing vehicle. Using the exemplary method according to the present invention, it is also believed to be possible to attain particularly reliable estimated values, for which a relatively small amount of computational work in a control unit may be necessary for this purpose. According to the exemplary method of the present invention, to satisfactorily estimate the transverse acceleration at the axle of the semitrailer/trailer, it is believed to be sufficient to ascertain (by measuring or estimating, as is explained below) the yaw velocity and the forward velocity of the towing vehicle. According to another exemplary method of the present invention, it is believed to be sufficient in comparable fashion to determine the forward velocity of the towing vehicle and the articulation angle between the towing vehicle and the semitrailer/trailer.
In accordance with the first exemplary method of the present invention, the transverse acceleration sought is determined as a function of the determined forward velocity of the towing vehicle and as a function of the determined yaw velocity of the towing vehicle. For this purpose, in an intermediate step, the articulation angle is first determined from the two input variables using equation 8, which is explained below. The transverse acceleration sought is ascertained as a function of the articulation angle and of the forward velocity, using equations 9 and 10, respectively, which are explained below.
In the second exemplary method of the present invention, where it is assumed that it is possible to measure or estimate the articulation angle, the forward velocity is also determined, either using a suitable sensor arrangement or structure or according to the abovementioned equation 8. Using the indicated equations 9 and 10, respectively, the two input variables, forward velocity and articulation angle, yield the transverse acceleration sought. With regard to the use of the term xe2x80x9cto determine,xe2x80x9d it should be indicated that forward velocity values and yaw velocity values are typically provided by other functions or components of an electronic stability program, i.e., are typically able to be measured. As such, the articulation angle can be estimated using the presently proposed exemplary method, provided that this is necessary, because the articulation angle is not necessarily or does not necessarily have to be made available by other electronic stability program components or electronic stability program functions. Furthermore, the articulation angle can in principle also be determined, for example, using a potentiometer, as referred to in the German Published Patent Application No. 39 23 677.
One concern, however, may be that this measuring principle may require devices at the towing vehicle and at the semitrailer or trailer.
Advantageously, the distance between the semitrailer/trailer axle and the trailer hitch or the kingpin of the towing vehicle may be taken into account when computationally correlating the yaw velocity and the forward velocity of the towing vehicle, as well as the articulation angle between the towing vehicle and semitrailer/trailer and the forward velocity.
According to another exemplary method of the present invention, when performing the computational correlation (relational operation), it is assumed that a transverse velocity existing at the semitrailer/trailer axle is equal to zero, or that the semitrailer/trailer axle does not have a slip angle. On the basis of this assumption, it is believed that a particularly simple, kinematic single-track model can be created for estimating the transverse acceleration at the semitrailer/trailer axle, since it is assumed to a certain extent here that the semitrailer or trailer xe2x80x9cis driven as if on a track.xe2x80x9d In what is believed to be a particularly significant situation pertaining to operating dynamics, namely in the case of an oversteering towing vehicle and a non-skidding semitrailer or trailer, this supposition is believed to be effectively satisfied, so that the transverse acceleration of the semitrailer/trailer axle can be particularly accurately estimated for the dangerous situations indicated at the outset.
According to another exemplary method according to the present invention, an articulation angle xcex94xcexa8 is estimated on the basis of its time derivative xcex94xcexa8, taking yaw velocities xcfx89Z, xcfx89A of the towing vehicle and semitrailer or trailer as a basis to obtain an estimated value xcex94xcexa8, where the yaw velocity xcfx89A of the semitrailer or trailer is represented in the form of:                     V        xZ                    1        A              ·    sin    ⁢      xe2x80x83    ⁢  Δ  ⁢      xe2x80x83    ⁢      Ψ    .  
The specified relations are believed to be particularly valid when the transverse velocity vKyZ of the towing vehicle at the kingpin or at the trailer hitch is disregarded.